Mechanical coolant pumps are directly driven by the internal combustion engine, for example, via a driving belt driving the pulley wheel of the coolant pump. If the pulley wheel is directly connected with the pump wheel, the pump performance depends on the rotational speed of the combustion engine. For allowing a more demand-responsive control of the coolant pump, mechanical coolant pumps can be provided with frictional clutches connecting the pulley wheel with the rotor shaft on demand only. The friction clutch is usually arranged in the dry section of the coolant pump.
DE 10 2006 039 680 A1 describes a switchable mechanical automotive coolant pump with the pump wheel being axially movable between a pumping position and a non-pumping position. The pump wheel is actuated by an actuator rod which is arranged concentrically with and inside of the hollow rotor shaft. This actuation arrangement is complex, expensive to produce, and leads to problems with respect to the sealing between the actuation rod and the rotor shaft.